Disturbed Mitochondrial Function Research Articles

Studies on the Mechanisms Causing Inhibition of Insulin Secretion in Rat Pancreatic Islets Exposed to Human Interleukin-1β Indicate a Perturbation in the Mitochondrial Function*

This study aimed at a more detailed characterization of the mechanisms by which interleukin 1 (IL-1) inhibits insulin secretion. For this purpose, isolated rat pancreatic islets were kept in tissue culture for 5 days in medium RPMI 1640 plus 10% calf serum. The islets were subsequently transferred to the same culture medium containing various test substances plus 1% human serum with or without 25 U/ml human recombinant IL-1 beta. After a culture period of 48 h the islet structure was examined in the electron microscope and the islet function studied in short term incubations in the absence of IL-1. Islets exposed to IL-1 showed ultrastructural signs of degeneration in 10-20% of the B cells while such changes were not found in other types of islet cells. An increased number of secondary lysosomes and occasional myelin figures were observed in the B cells exposed to IL-1. These ultrastructural alterations were, however, reversed in islets cultured in cytokine-free medium for 6 days after the IL-1 treatment. In islets cultured in the presence of 11.1 mM glucose only, or 11.1 mM glucose plus 10 mM nicotinamide, 61 mM dimethyl area, 2 micrograms/ml indomethacin, 10 microM 4-bromophenacyl bromide or 10 microM nordihydroguaiaretic acid, 10 microM phenantroline, and 0.1 or 1.0 microgram/ml cyclosporin A, IL-1 reduced the insulin release by 64-85%. Culture at 5.6 mM glucose did not modify the IL-1-induced inhibition of insulin release, whereas a significant protective effect was observed at 28 or 56 mM glucose. The DNA content in IL-1-exposed islets cultured at 11.1 mM glucose was decreased by about 20% but not in islets cultured at other glucose concentrations. The D-[5-3H]glucose utilization at 16.7 mM glucose was unaffected by IL-1, whereas the oxidation of D-[6-14C]glucose was reduced by 50%. The present results suggest that IL-1-induced inhibition of insulin secretion is related to a disturbed mitochondrial function. This effect is not counteracted by a poly(ADP-ribose) synthetase inhibitor, a hydroxyl radical scavenger, an iron chelator, a T lymphocyte-specific immunosuppressive drug, or inhibitors of phospholipase A2 or inhibitors of prostaglandin and leukotriene synthesis. Thus, IL-1-induced inhibition of insulin secretion seems not to be mediated by the same mechanisms as those causing alloxan- or streptozotocin-induced damage of B cells. Furthermore, the action of IL-1 does not appear to be mediated via arachidonic acid metabolism. Glucose affords some protection, probably by enhancing the B cell mitochondrial function.(ABSTRACT TRUNCATED AT 400 WORDS)

Photodynamic effects of hematoporphyrin derivative on the uptake of rhodamine 123 by mitochondria of intact murine L929 fibroblasts and Chinese ovary K1 cells.

Abstract— It was shown that the cationic fluorescence probe rhodamine 123 accumulates in mitochondria of murine L929 fibroblasts and Chinese hamster ovary Kl epithelial cells due to the driving force of both plasma membrane and mitochondrial membrane potentials. Photodynamic treatment of L929 cells with hematoporphyrin derivative resulted in an increased uptake of rhodamine 123 and a diminished uptake of 1,1,3,3,3′,3′‐hexamethylindocarbocyanine iodide. This indicates a considerably increased mitochondrial membrane potential, which most likely is the result of a direct or secondary inhibition of the ATP‐synthetase, and a decreased plasma membrane potential. The oxygen consumption rate and the ATP level decreased due to photodynamic treatment. Post‐incubation of L929 cells subsequent to photodynamic treatment revealed that the uptake of rhodamine 123. the ATP content and the oxygen consumption rate were restored. For all parameters similar results were obtained with CHO‐K1 cells, with the exception that during post‐incubation the intracellular ATP content remained at the level reached after illumination. These results indicate that photodynamically induced disturbance of mitochondrial functions and the ATP level are not crucial for the loss of clonogenicity of L929 cells. In CHO‐K1 cells however, the continuously lowered ATP level may have detrimental consequences for cell survival. The photodynamic stimulation of the rhodamine 123 uptake may be a rather general phenomenon. Because rhodamine 123 exhibits a much higher toxicity towards carcinoma cells than towards other cells, a synergistic interaction between this drug and photodynamic therapy (PDT) may be anticipated, if PDT also stimulates mitochondrial rhodamine 123 accumulation in carcinoma in vivo.

Relationship between regional myocardial blood flow and tissue ATP content in acute ischemia.

This study was undertaken to determine the relationships between myocardial mitochondrial function, regional myocardial blood flow (MBF), and tissue ATP content in acute ischemia. Fifty-one anesthetized dogs were used in the tests. MBF was measured by the H2 gas clearance method in order to define the ischemic area, during periods of coronary occlusion of 10, 20, 60, and 90 min. The correlation between MBF and myocardial ATP content in the ischemic area was positive and significant in each group (r = 0.54-0.82). The ATP content in the true ischemic area (where MBF was less than 20 ml/min/100 Gm) decreased significantly even after 10 min of occlusion, but mitochondrial function decreased only after 20 min of coronary occlusion when compared to the nonischemic area. Although ischemia induces mitochondrial dysfunction, a very short period of ischemia did not cause significant disturbance of mitochondrial function. Moreover, in the areas with MBF of 20-40 ml/min/100 Gm, the ATP content began to decrease 60 min after occlusion, whereas 10 or 20 min of occlusion did not reduce the ATP content. These results suggest that normal maintenance of ATP levels depends not only on MBF itself but also on the duration of ischemia plus the degree of damage to mitochondrial function, and that critical blood flow, defined as the minimum flow necessary to maintain the level of myocardial ATP, varies with the duration of ischemia.

Mechanism of chlorpromazine-induced arrhythmia arrhythmia and mitochondrial dysfunction

In this study, we investigated the mechanism of the arrhythmogenic action of chlorpromazine (CPZ). Thirty-two anesthetized mongrel dogs were used. In each, the chest was opened and a stimulating electrode was attached to the apex of the left ventricle and the ventricular multiple response threshold (VMRT) was measured. The carotid artery was cannulated to measure aortic pressure. The dogs were divided into four groups, and the time course of VMRT, blood pressure, and heart rate were determined. All groups were placed under observation for 30 min after CPZ infusion. In the control group, only saline (2ml/kg) was infused; CPZ group: CPZ (Img/kg) was infused 10 min after saline (2ml/kg) infusion; CoQ10 group: Coenzyme Q10 (CoQ10) (5mg/kg) was infused 10 min before CPZ (Img/kg) infusion; FAD group: Flavin-adenine-dinucleotide (FAD) (2mg/kg) was infused 10 min before CPZ (Img/kg) infusion. In each group, myocardial mitochondria were prepared 30 min after CPZ infusion. The mitochondrial functions, respiratory control index, AdP/O, State III rate of oxygen consumption, and activities of two segments of the electron-transport chain (NADH leads to CoQ leads to cyt.c and cyt.c leads to cyt.a,a3 leads to O2) were measured separately. Ca++--binding activity of the mitochondria was also determined. CPZ administration decreased VMRT and blood pressure, and caused mitochondrial dysfunction which derived from a disturbance in the first segment of the electron transport chain. Decreased Ca++--binding activity was observed when mitochondrial function was disturbed. CoQ10 prevented significantly the decrease in VMRT and the disturbance of mitochondrial function induced by CPZ, but did not prevent the hypotensive effect of CPZ. FAD prevented not only the decrease in VMRT and the disturbance of mitochondrial function, but also the hypotensive effect of CPZ. These results suggest that the decrease in VMRT is closely related to mitochondrial dysfunction induced by CPZ. Moreover, it is suggested that the arrhythmogenic effect of CPZ is derived from the decreased mitochondrial Ca++--binding activity.

Mitochondrial functions in chronic spinal muscular atrophy.

We determined the respiration rate, respiratory control and ADP/O ratios, with different substrates in mitochondria isolated from seven patients with chronic spinal muscular atrophy and compared them with normal human muscle. In all cases studied, a severe alteration of the respiratory control with variable derangement of oxidative phosphorylation was found. Similar findings have been described in other neuromuscular disorders including the so-called "mitochondrial myopathy". We believe that this disturbance of mitochondrial function is non specific and only the hypermetabolic syndrome of Luft could be considered biochemically as a "mitochondrial myopathy", a disorder selectively involving mitochondria of skeletal muscle.

Janus Green B Causing Functional Disturbances in Mitochondria in Mg<SUP>2+</SUP>-containing Medium

The effect of Janus green B was investigated on respiration and oxidative phosphorylation of isolated rat liver mitochondria with and without magnesium ions. Janus green B in medium with magnesium ions stimulated state 4-respiration, inhibited oxidative phosphorylation and induced swelling of the mitochondrial matrix. This dye also suppressed the arsenate-and calcium-stimulated respiration of mitochondria. Such disturbances of mitochondrial function by Janus green B were rarely observed in the absence of magnesium ions. It can be concluded that the swelling of mitochondria and the inhibition of oxidative phosphorylation by Janus green B were clearly related to magnesium ions.

Mitochondrial functions in five cases of human neuromuscular disorders.

We determined the respiration, respiratory control, and Pi:O ratios with different substrates in mitochondria isolated from five cases of human neuromuscular disorders (two cases of central core disease, two cases of neuropathy of Dejerine-Sottas, and one case of Kugelberg-Welander's disease) and compared them with normal human muscle. In all the myopathies studied, a severe derangement of the respiratory control with variable derangement of oxidative phosphorylation was found. This supports the idea that a group of neuromyopathies shares the same biochemical lesion as the so-called mitochondrial myopathies, forming with them a group of myopathies which may be related through a similar biochemical lesion of varying degree. Alternatively, disturbance of mitochondrial functions in a number of myopathies could be considered as a non-specific finding.